DETERMINATION OF THE DENSITY-OF-STATES IN AMORPHOUS SILICON-CARBON ALLOYS USING A FOURIER TRANSFORMATION OF TRANSIENT PHOTOCURRENT DATA

Transient photocurrent decay measurements have been performed on a ser ies of amorphous silicon-carbon alloys, A numerical Fourier transform procedure has been employed to convert these data into the frequency d omain, and the results have subsequently been analysed using a procedu re developed for the study of modulated photocurrents. This process ha s allowed determination of the distribution of gap states in the films as a function of carbon concentration. Results illustrate an increasi ng density of conduction band tail states and a significant increase i n the number of deeper states (situated 0.5-0.7 eV below the conductio n band mobility edge) as carbon content increases. While the former in formation suggests a shift of the band tail to deeper in the gap, with no significant change in slope, the latter demonstrates an overall br oadening of the deep states (usually ascribed to D- dangling bond defe cts) with carbon content. The data obtained by this novel technique ar e compared with those obtained from time-of-flight experiments.